Net calorific value for various types of wood, source: Technologie- und Förderzentrum (Technology and Support Centre) (TFZ)
Straubing, Bavaria, Germany
Water content in %
0
10
20
30
40
50
Type of tree
Unit of measurement
Spruce
kWh/kg
5.20
4.64
4.05
3.44
2.86
2.27
kWh/smt
2245
2020
1979
1863
1805
1726
kWh/stcm
1249
1177
1096
1039
1005
958
kWh/tcm
925
872
812
770
745
709
Scots pine
kWh/kg
5.33
4.75
4.14
3.53
2.94
2.33
kWh/smt
2613
2441
2239
2170
2114
2009
kWh/stcm
1454
1354
1243
1209
1170
1116
kWh/tcm
1077
1003
921
895
867
827
Beech
kWh/kg
11.00
4.53
3.97
3.39
2.81
2.22
kWh/smt
3475
3187
2899
2704
2609
2482
kWh/stcm
1757
1613
1458
1361
1315
1252
kWh/tcm
1432
1314
1188
1109
1072
1020
Oak
kWh/kg
5.00
4.50
3.92
3.33
2.66
2.19
kWh/smt
3336
3091
2836
2760
2576
2543
kWh/stcm
1687
1557
1432
1396
1349
1283
kWh/tcm
1375
1269
1166
1138
1099
1045
Relation of moisture content (w) to moisture level in fuel (u)
The proportion of water in woodchips and wood pellets is given as
either the moisture content or the fuel moisture level. The moisture
content (in %) is relative to the moist fuel mass or the fresh sub-
stance (FS); the fuel moisture level is relative to the absolutely dry
fuel mass (TS).
Example:
If 100 kg of fuel contains 50 kg of water, the fuel has a moisture con-
tent of 50 % (w50) and a fuel moisture level of 100 % (u = 100).
u [%]
=
w [%]
x 100
100 ― w [%]
0
20
40
60
80
100
120
140
160
180
200
0
10
20
30
40
50
60
70
Fuel moisture level (u) in %
Water content (w) in %
Determining the amount of fuel required
The amount of fuel required can be calculated on the basis of the net
calorific value and the required rated heating output. Significant influ-
encing factors for this are the moisture content of the fuel and the
efficiency of the system.
B
=
Q
N
H
u
x η
Principles of wood combustion
(cont.)
VITOFLEX 300-UF
Viesmann
7
5682428
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